The service provided for each user by a wireless cellular network needs to meet certain Quality of Service (QoS) requirement; and the QoS mainly depends on the Signal-to-Interference Ratio (SIR) of the signal received by each user. With a Wideband Code Division Multiple Access (WCDMA) system as an example, respective users in a same cell occupy the same frequency band and time and are isolated from one another only by the orthogonality of spreading codes. Whereas, due to multiple paths, delay and the like of a wireless channel, the cross correlation among the users is not ideal, and other users may interfere the current user. Thereby, more interference may be caused to the current user and the SIR of the signal received by the current user may decrease when the number of users in the cell or the power of other users increases; and when the interference reaches a certain extent, the current user cannot communicate normally. Therefore, the WCDMA system is severely limited by the interference, and the magnitude of the interference directly affects the capacity of the system. To solve the problem, the 3rd Generation Partnership Project (3GPP) protocol defines several power control methods; and the power control aims to adjust the transmission power of each user to compensate for channel fading and offset near-far effect and further aims to maintain the transmission power of each user to be above the minimum standard required by the communication, thus, the interference to other users can be reduced greatly, and accordingly, the capacity of the system is improved.
The inner loop and closed loop power control of a WCDMA system is completed by User Equipment (UE) and a cell in an active set, as shown in FIG. 1, the process is as follows: the cell measures the SIR of an uplink Dedicated Physical Channel (DPCH) in real time, and compares the measured SIR with a target SIR (SIR_target); and if the measured SIR is smaller than the SIR_target, it is indicated that the uplink channel quality is poor, and the cell sends a power control instruction to instruct the UE to increase the transmission power. On the contrary, if the measured SIR is greater than the SIR_target, it is indicated that the uplink channel quality is better than expected quality, and the cell sends a power control indication to instruct the UE to decrease the transmission power in order to save power resources, decrease the interference to other users and improve the capacity of the system. When in a soft handover status, the UE communicates with multiple cells at the same time, so the UE may receive different power control commands. In such a circumstance, the UE may decrease the transmission power only if one power control indication requires the UE to decrease the transmission power; and the UE may not increase the transmission power until all the power control instructions received by the UE require the UE to increase the transmission power.
In the existing inner loop and closed loop power control method, if the UE is in the soft handover status, when an uplink and a downlink are unbalanced, the decoding of an uplink control channel, particularly decoding of an uplink High Speed Dedicated Physical Control Channel (HS-DPCCH) of the serving High-Speed Downlink Shared Channel (HS-DSCH) cell may become unreliable, which affects the QoS.
For example, in a Heterogeneous Network (HetNet), when the UE is in a soft handover area of a macro NodeB and a low power NodeB, and the serving HS-DSCH cell of the UE is a cell in the macro NodeB, the signal received by the low power NodeB from the UE may be much better than that received by the macro NodeB from the UE due to the unbalance between the uplink and the downlink. Then, it is possible that the inner loop and closed loop power control indication received by the UE from the cell in the macro NodeB requires the UE to increase the transmission power, but the inner loop and closed loop power control indication received by the UE from the cell in the low power NodeB requires the UE to decrease the transmission power. According to the existing inner loop and closed loop power control combination principle, the UE may decrease the transmission power only if one power control indication received by the UE requires to decrease the transmission power, so the signal received by the macro NodeB from the UE may become worse. At the moment, the decoding of an uplink control channel, particularly that of an HS-DPCCH of the serving HS-DSCH cell from the UE to the macro NodeB is unreliable, which affects the QoS of the HSDPA seriously. This is because the HS-DPCCH contains a hybrid automatic repeat acknowledgement message (generally represented by ACK/NACK) and downlink Channel Quality Indicator (CQI) information, the decoding error of the ACK/NACK may cause the packet loss of High Speed Downlink Packet Access (HSDPA) or add unnecessary retransmission, and the decoding error of the CQI may cause the block scheduled by the HSDPA to become too large to be decoded correctly or become too small to waste resources.
In a word, according to the existing inner loop and closed loop power control method, when UE is in a soft handover process and an uplink and a downlink are unbalanced, it is possible that the decoding of an uplink control channel, particularly the decoding of an HS-DPCCH of a serving HS-DSCH cell is unreliable, thereby affecting the QoS.